[Bug] MCP prompt arguments receive literal $1/$2 placeholders instead of user input — type validation fails

[michael-conrad]

Description

This error fires at startup, not on interactive use. When opencode discovers an MCP server that exposes prompts with typed arguments (e.g. precision: int), it calls prompts/get during initialization to resolve prompt templates for command registration. The $1/$2 placeholders are sent as literal argument values during this startup probe, and the MCP server's typed argument validation rejects them.

Example error from mcp-mathematics at startup:

MCP error 0: Could not convert argument 'precision' with value '$2' to expected type int
MCP error 0: Could not convert argument 'batch_size' with value '$1' to expected type int
failed to getPrompt

The prompts/get JSON payload confirms the literal placeholder is being sent:

{
    "method": "prompts/get",
    "params": {
        "name": "scientific_calculation",
        "arguments": {
            "precision": "$2",
            "calc_type": "general",
            "show_steps": false
        }
    }
}

This was previously reported in #9776 (auto-closed due to inactivity) and confirmed by another user in #9776 (comment) who captured the same "$1" in the prompts/get payload.

The root cause is in packages/opencode/src/command/index.ts lines 100-112. The get template() function maps prompt arguments to $N placeholders but never substitutes them against actual user-provided command arguments before calling mcp.getPrompt().

Plugins

None

OpenCode version

1.14.33

Steps to reproduce

1. Configure an MCP server that exposes prompts with typed arguments (e.g. mcp-mathematics via uvx mcp-mathematics)
2. Start opencode
3. The error appears in the startup log automatically — no user interaction required

Screenshot and/or share link

N/A

Operating System

Ubuntu 24.04.4 LTS, Linux 6.8.0-124-generic x86_64

Terminal

WezTerm

Full startup log

2026-06-24T00:38:58.314570Z  INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:38:58 +1350ms service=mcp clientName=math promptName=scientific_calculation error=MCP error 0: Could not convert argument 'precision' with value '$2' to expected type typing.Annotated[int, 'Decimal precision for results']. Error: 1 validation error for int
2026-06-24T00:38:58.314591Z  INFO sidecar: opencode_lib::cli:   Input should be a valid integer, unable to parse string as an integer [type=int_parsing, input_value='$2', input_type=str]
2026-06-24T00:38:58.314595Z  INFO sidecar: opencode_lib::cli:     For further information visit https://errors.pydantic.dev/2.13/v/int_parsing failed to getPrompt
2026-06-24T00:38:58.314908Z  INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:38:58 +0ms service=mcp clientName=math promptName=batch_calculation error=MCP error 0: Could not convert argument 'batch_size' with value '$1' to expected type typing.Annotated[int, 'Number of calculations to process']. Error: 1 validation error for int
2026-06-24T00:38:58.314927Z  INFO sidecar: opencode_lib::cli:   Input should be a valid integer, unable to parse string as an integer [type=int_parsing, input_value='$1', input_type=str]
2026-06-24T00:38:58.314933Z  INFO sidecar: opencode_lib::cli:     For further information visit https://errors.pydantic.dev/2.13/v/int_parsing failed to getPrompt
2026-06-24T00:38:58.487985Z  INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:38:58 +173ms service=server error=Session not found failed
2026-06-24T00:38:59.379392Z  INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:38:59 +892ms service=server error=NotFoundError failed
2026-06-24T00:39:06.830627Z  INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:39:06 +7451ms service=file.watcher dir=/home/muksihs cause=TimeoutError: TimeoutError
2026-06-24T00:39:06.830645Z  INFO sidecar: opencode_lib::cli:     at orElse (/$bunfs/root/chunk-y3yhj99w.js:25:15739)
2026-06-24T00:39:06.830648Z  INFO sidecar: opencode_lib::cli:     at runLoop (/$bunfs/root/chunk-y3yhj99w.js:25:2045)
2026-06-24T00:39:06.830651Z  INFO sidecar: opencode_lib::cli:     at evaluate (/$bunfs/root/chunk-y3yhj99w.js:25:1435)
2026-06-24T00:39:06.830653Z  INFO sidecar: opencode_lib::cli:     at <anonymous> (/$bunfs/root/chunk-y3yhj99w.js:25:5589)
2026-06-24T00:39:06.830656Z  INFO sidecar: opencode_lib::cli:     at FileWatcher.state (/$bunfs/root/chunk-aan3zwa9.js:7:67961)
2026-06-24T00:39:06.830659Z  INFO sidecar: opencode_lib::cli:     at FileWatcher.state (definition) (/$bunfs/root/chunk-14sjmzy6.js:444:5415)
2026-06-24T00:39:06.830661Z  INFO sidecar: opencode_lib::cli:     at FileWatcher.init (/$bunfs/root/chunk-14sjmzy6.js:2722:9592)
2026-06-24T00:39:06.830664Z  INFO sidecar: opencode_lib::cli:     at FileWatcher.init (definition) (/$bunfs/root/chunk-14sjmzy6.js:444:6981)
2026-06-24T00:39:06.830667Z  INFO sidecar: opencode_lib::cli:     at InstanceBootstrap.init (/$bunfs/root/chunk-14sjmzy6.js:2722:9613)
2026-06-24T00:39:06.830670Z  INFO sidecar: opencode_lib::cli:     at InstanceBootstrap (/$bunfs/root/chunk-14sjmzy6.js:2722:9779)
2026-06-24T00:39:06.830674Z  INFO sidecar: opencode_lib::cli:     at InstanceStore.boot (/$bunfs/root/chunk-aan3zwa9.js:18:5242)
2026-06-24T00:39:06.830677Z  INFO sidecar: opencode_lib::cli:     at InstanceStore.load (/$bunfs/root/chunk-aan3zwa9.js:18:6366) failed to subscribe
2026-06-24T00:39:07.095955Z  INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:39:07 +265ms service=file.watcher dir=/home/muksihs/git/opencode-config cause=TimeoutError: TimeoutError
2026-06-24T00:39:07.095979Z  INFO sidecar: opencode_lib::cli:     at orElse (/$bunfs/root/chunk-y3yhj99w.js:25:15739)
2026-06-24T00:39:07.095984Z  INFO sidecar: opencode_lib::cli:     at runLoop (/$bunfs/root/chunk-y3yhj99w.js:25:2045)
2026-06-24T00:39:07.095990Z  INFO sidecar: opencode_lib::cli:     at evaluate (/$bunfs/root/chunk-y3yhj99w.js:25:1435)
2026-06-24T00:39:07.095994Z  INFO sidecar: opencode_lib::cli:     at <anonymous> (/$bunfs/root/chunk-y3yhj99w.js:25:5589)
2026-06-24T00:39:07.095999Z  INFO sidecar: opencode_lib::cli:     at FileWatcher.state (/$bunfs/root/chunk-aan3zwa9.js:7:67961)
2026-06-24T00:39:07.096004Z  INFO sidecar: opencode_lib::cli:     at FileWatcher.state (definition) (/$bunfs/root/chunk-14sjmzy6.js:444:5415)
2026-06-24T00:39:07.096010Z  INFO sidecar: opencode_lib::cli:     at FileWatcher.init (/$bunfs/root/chunk-14sjmzy6.js:2722:9592)
2026-06-24T00:39:07.096016Z  INFO sidecar: opencode_lib::cli:     at FileWatcher.init (definition) (/$bunfs/root/chunk-14sjmzy6.js:444:6981)
2026-06-24T00:39:07.096021Z  INFO sidecar: opencode_lib::cli:     at InstanceBootstrap.init (/$bunfs/root/chunk-14sjmzy6.js:2722:9613)
2026-06-24T00:39:07.096027Z  INFO sidecar: opencode_lib::cli:     at InstanceBootstrap (/$bunfs/root/chunk-14sjmzy6.js:2722:9779)
2026-06-24T00:39:07.096032Z  INFO sidecar: opencode_lib::cli:     at InstanceStore.boot (/$bunfs/root/chunk-aan3zwa9.js:18:5242)
2026-06-24T00:39:07.096038Z  INFO sidecar: opencode_lib::cli:     at InstanceStore.load (/$bunfs/root/chunk-aan3zwa9.js:18:6366) failed to subscribe
2026-06-24T00:39:17.098010Z  INFO sidecar: opencode_lib::cli: ERROR 2026-06-24T00:39:17 +10002ms service=file.watcher dir=/home/muksihs/git/opencode-config/.git cause=TimeoutError: TimeoutError
2026-06-24T00:39:17.098031Z  INFO sidecar: opencode_lib::cli:     at orElse (/$bunfs/root/chunk-y3yhj99w.js:25:15739)
2026-06-24T00:39:17.098034Z  INFO sidecar: opencode_lib::cli:     at runLoop (/$bunfs/root/chunk-y3yhj99w.js:25:2045)
2026-06-24T00:39:17.098037Z  INFO sidecar: opencode_lib::cli:     at evaluate (/$bunfs/root/chunk-y3yhj99w.js:25:1435)
2026-06-24T00:39:17.098039Z  INFO sidecar: opencode_lib::cli:     at <anonymous> (/$bunfs/root/chunk-y3yhj99w.js:25:5589)
2026-06-24T00:39:17.098042Z  INFO sidecar: opencode_lib::cli:     at FileWatcher.state (/$bunfs/root/chunk-aan3zwa9.js:7:67961)
2026-06-24T00:39:17.098045Z  INFO sidecar: opencode_lib::cli:     at FileWatcher.state (definition) (/$bunfs/root/chunk-14sjmzy6.js:444:5415)
2026-06-24T00:39:17.098048Z  INFO sidecar: opencode_lib::cli:     at FileWatcher.init (/$bunfs/root/chunk-14sjmzy6.js:2722:9592)
2026-06-24T00:39:17.098051Z  INFO sidecar: opencode_lib::cli:     at FileWatcher.init (definition) (/$bunfs/root/chunk-14sjmzy6.js:444:6981)
2026-06-24T00:39:17.098054Z  INFO sidecar: opencode_lib::cli:     at InstanceBootstrap.init (/$bunfs/root/chunk-14sjmzy6.js:2722:9613)
2026-06-24T00:39:17.098057Z  INFO sidecar: opencode_lib::cli:     at InstanceBootstrap (/$bunfs/root/chunk-14sjmzy6.js:2722:9779)
2026-06-24T00:39:17.098060Z  INFO sidecar: opencode_lib::cli:     at InstanceStore.boot (/$bunfs/root/chunk-aan3zwa9.js:18:5242)
2026-06-24T00:39:17.098066Z  INFO sidecar: opencode_lib::cli:     at InstanceStore.load (/$bunfs/root/chunk-aan3zwa9.js:18:6366) failed to subscribe
2026-06-24T00:39:32.143253Z  INFO opencode_lib: Received Exit
2026-06-24T00:39:32.143269Z  INFO opencode_lib: Killed server